The invention relates to an apparatus for monitoring a print result in a rotary printing press, comprising:                a web monitoring system including a matrix camera that is movable in transverse direction across a web being printed in the printing press, the matrix camera being adapted to capture an excerpt of a printed image in synchronism with a repeat of the printed image during a production run of the printing press; and        an inspection system for a complete inspection of the printed image, said inspection system including a line camera that extends over the entire width of the web.        
For the printing industry, web monitoring systems have been known which permit to monitor a selected excerpt from the image printed onto the web during a production run. By synchronising the matrix camera with the repeat of the printed image it can be achieved that a stationary image which represents the selected excerpt of the printed image can be presented to the operator on a monitor. When the monitoring of this excerpt reveals that the printed image suffers from certain errors, e.g. register errors, the operator can re-adjust the pertinent settings of the printing press, such as the side register or the longitudinal register of individual colour decks, in order to correct these errors. Similarly, other setting parameters of the printing press may be re-adjusted in order to remedy other types of error, e.g. as the impression setting (the force with which the form cylinder is pressed against the web).
A control desk including at least one monitor and operating elements for controlling the matrix camera and for inputting the set operations that may be necessary for the printing press forms part of the web monitoring system.
Typically, the matrix camera has a zoom function, so that defective or problematic areas of the printed image can be assessed with high resolution.
However, the matrix camera permits only to monitor a relatively small fraction of the entire surface of the printed web, typically a fraction in the order of magnitude of about 1%. With a conventional web monitoring system, it is therefore not possible to reliably detect every error that occurs in the printed product.
Special inspection systems have been developed for a complete inspection of the printed product, these systems being capable of capturing a complete image of the printed web and storing the same in digital form. The image information is linked with positional information indicating the location of the respective image area in longitudinal direction of the web. A control desk with a monitor permits to retrieve, for any desired point on the printed web, the corresponding image and to inspect the same for errors. When non-tolerable errors are found in the printed image, it is possible on the basis of the stored positional information to access the defective portion of the printed web by means of a winder and to excise this portion from the web after the print run has been terminated.
Error recognition algorithms for automatically recognizing errors have also been developed. To that end, the first approximately 50 repeating printing images (formats), for example, are digitally captured with a line camera, and the image information is integrated over the 50 images, so that one obtains a reference image, the so-called “golden image” with which the images that are captured later during the print run are to be compared. In the integration phase, the range of variance of the image information may be determined for each pixel, so that tolerance limits for error recognition can be set. During the print run, the image that is currently being captured is subtracted from the reference image, and when the difference obtained is outside of the error tolerances, an error signal is generated and the defective image area is shown on the monitor of the control desk. This enables the operator to intervene already during the print run in order to remove the error or, when the error is not removable, to abort the print run. Moreover, the positions of the image errors that have been recognized may be stored, so that the defective places on the printed web may deliberately be inspected after termination of the print run and may be removed if necessary. The final decision whether a defective image area is to be removed or can still be tolerated is still taken by the operating personal.
Until now, even when web monitoring systems and inspection systems are employed simultaneously with the same printing press, these systems are generally configured as separated, independent systems.
On the other hand, inspection systems have become known which have a high-resolution digital line camera the image signal of which can also be used for web monitoring. However, this line camera does not have an optical zoom function, so that the resolution is limited and problematic image areas may often not be inspected with the desired accuracy.
For an inspection system with automatic error recognition, there has already been developed an interface to a web monitoring system, which interface permits to alert the operator at the control desk of the web monitoring system of errors that have been recognized by the inspection system.